1. Field of the Invention
The present invention relates to a fuel cell formed by sandwiching an electrolyte electrode assembly between a first metal separator and a second metal separator. The electrolyte electrode assembly includes a pair of electrodes, and an electrolyte interposed between the electrodes.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a solid polymer electrolyte membrane. The solid polymer electrolyte membrane is a polymer ion exchange membrane, and interposed between an anode and a cathode to form a membrane electrode assembly (electrolyte electrode assembly). Each of the anode and the cathode includes an electrode catalyst layer and porous carbon. The membrane electrode assembly is sandwiched between a pair of separators (bipolar plates). The membrane electrode assembly and the separators make up a power generation cell for generating electricity. In use, typically, a predetermined number of power generation cells are stacked together to form a fuel cell stack.
In the fuel cell, a flow field for supplying a fuel gas (hereinafter also referred to as the reactant gas) is formed on a separator surface facing the anode, and a flow field for supplying an oxygen-containing gas (hereinafter also referred to as the reactant gas) is formed on a separator surface facing the cathode. Further, a flow field for supplying a coolant is formed between separators for each power generation cell or for every predetermined number of power generation cells.
In general, the fuel cells adopts, so called, internal manifold structure in which fluid supply passages and fluid discharge passages extend through the separators in the stacking direction. The fluids, i.e., the fuel gas, the oxygen-containing gas, and the coolant are supplied from the respective fluid supply passages to the fuel gas flow field, the oxygen-containing gas flow field, and the coolant flow field, and then, discharged into the respective fluid discharge passages.
In the case where metal separators are used as the separators, since the fluid supply passages and the fluid discharge passages cannot be formed in the metal separators directly, various designs are adopted.
For example, as shown in FIG. 12, a fuel cell separator disclosed in Japanese Laid-Open Patent Publication No. 2005-267912 includes a central member 1 comprising a metal member, an outer member 2 comprising a resin member provided around the central member 1, and a joint member 3 comprising a resin member interposed between the central member 1 and the outer member 2. The joint member 3 at least covers an area near an outer edge 1a of the central member 1 and an inner edge 2a of the outer member 2. A channel 4 for oxygen and water produced in power generation is formed in the outer member 2, and ribs 5 are formed in the joint member 3 to cover the channel 4.
In the conventional technique, the outer member 2 is joined to the outer portion of the central member 1 through the joint member 3. For example, the joint member 3 is made of thermosetting resin such as silicone rubber. The outer member 2 is made of thermoplastic resin such as engineering plastic. That is, in the outer portion of the metal separator as the central member 1, the resin member as the outer member 2 and the resin joint member as the joint member 3 are provided. Therefore, in the presence of the resin joint member, the strength of the separator becomes low, and the durability of the separator becomes low undesirably.